Many problems exist in city heating source and network such as low transmission capacity,inability to reach the expected value for the operation of heat source,impossibility to adjust the load of large peak heat source timely and frequently,etc..In view of this,medium and small boilers could be considered the peak load regulating heat source and CHP the main heat source to have the combined heating supplies.The peak load of medium and small boilers has been determined, the life cycle costs of different peak shaving coefficients have been compared and the outdoor operation temperature for the medium and small boilers has been worked out.Results show that the new scheme is more economic.